Process of making fasteners



April 1941. G. H. c. CORNER 2,239,645

PROCESS OF MAKING FASTENERS Filed June 17, 1938 INVENTOR. GewyeH Cf Lorner ATTORNEYS.

Patentecl Apr. 22, 1941 PROCESS OF MAKING FASTENERS George Henry Clifiord Corner, Sutton Goldfield, England, assignor to Talon, Inc., a corporation of Pennsylvania Application June 17, 1938, Serial No. 214,277 In Great Britain July 22, 1937 2 Claims.

This invention relates to the manufacture of sliding clasp fasteners of the well known type in which fastener members secured to two mounting tapes are brought into interlocking engagement by a slider mounted on the stringers. In particular, the invention relates to the manufacture of separable fasteners of the type described in which the fastener members are made from non-metallic material.

It has already been proposed to make fastener members of the type described from artificial resin material by casting directly on to the tape. In this process it has hitherto been necessary that the thermoplastic material should be brought to a high degree of fluidity during the casting operation in order that the bond between the fastener members and the tape may be sufficiently strong. The necessary fluidity results in excess of the thermoplastic material being squeezed out of the mold onto the portions of the tape between the fastener members, and the resultant flash impairs the flexibility of the tape. Flash may also be formed on the body of the individual members by the squeezing out of fluid material at the joints between the separable mold parts. Moreover, the production of thermoplastic members of good durability involves th employment of materials having a high softening point, and consequently in order to obtain a sufficient degree of fluidity in the casting operation it is necessary to use relatively high temperatures which may have a harmful action on the material of the mounting tape.

The object of this invention is to provide a process of manufacturing the fastener stringers in which the fastener members are cast directly on the mounting tape, and which does not suffer from the stated disadvantages.

In Corner Patent No. 1,920,138 there is described a process of manufacturing separable fasteners in which fastener members produced from suitable non-metallic material are firmly attached to the fabric tape by cementing, gluing or by temporarily softening the material of the fastener member jaws sufficiently to make them adhere to the tape.

According to the present invention. fastener members of suitable thermoplastic material are cast, either singly or in rows, directly on the fabric mounting tape and the stringers thus formed are submitted to the action of a solvent whereby the jaws or like attaching surfaces of the fastener members are temporarily softened to make them adhere more firmly to the tape.

In the accompanying drawing:

Fig. 1 shows schematically how a fastener stringer may be dipped in a solvent bath;

Fig. 2 is a cross-section at right angles to Fig. 1.

In a preferred embodiment of the invention, only the fabric stringer tapes 3 ar subjected to the direct action of the solvent bath 4, the operation being conducted in such a manner that the external surfaces of the fastener members 5 are not brought into direct contact with the solvent to any substantial extent. The inner surface of the material of the jaws 6 of the members is, however, temporarily softened by solvent which is transmitted through the stringer tape by capillary action. This embodiment of the invention presents the advantage that it. minimizes the risk of cracking of the molded fastener members which is liable to occur when the fastener members are themselves dipped or otherwise brought into direct contact with the solvent. This cracking of the fastener members may take the form of internal fracture and is possibly due to the release, by the action of the solvent, of internal stresses set up in the material during the molding operation.

The temperatures in the casting operation may be, and preferably are, sufiiciently low to avoid any risk of tendering the fabric of the tape and to prevent the thermoplastic material from attaining a degree of fluidity likely to result in the production of flash. Such temperatures do not of themselves afford such a good bond between the fastener members and the tape as temperatures of a. somewhat higher order, but the strength of the bond is increased considerably by the subsequent treatment with a solvent in accordance with this invention, and the finished fastener has a strength comparable with or even better than the strength of fasteners made by casting at relatively high temperatures.

Similarly it is possible to use lower pressures than would have been necessary in processes hitherto proposed for casting fasteners, since it is only necessary to employ a pressure high enough to form the members to the desired shape. This, of course, also assists in the reduction of flash.

Any suitable thermoplastic material which is capable of being temporarily softened by a solvent may be employed for thepurposes of this invention. Thus, for example, there may be used cellulose ester or ether compositions particularly cellulose acetate compositions, or compositions based on resinous polymerised unsaturated organic compounds e. g. polymerised vinyl derivatives or polymerised acrylic acid or methacrylic acid derivatives. Not all these materials are suitable for separable fasteners for all purposes, but those skilled in the art will naturally choose a material most suitable for the purpose to be served. In the same way the choice of a solvent will depend on its suitability as it appears to the person skilled in the art, due account being taken of its solvent effect on the thermoplastic material and its effect on the tape. It is essential that in the finished fastener the fabric tape between the fastener members should retain sufficient flexibility for it to act in a hinge-like manner and any cementing composition intended to be applied for the purpose of the invention must therefore be chosen from materials which do not unduly stiffen the fabric tape.

In certain circumstances, depending upon the nature of the particular thermoplastic material and upon the molding conditions, it may he satisfactory to pass the stringer through a bath of solvent in such a manner that the whole or part of the fastener member is immersed therein, subsequently allowing the solvent to evaporate.

Irrespective of which of the particular methods above referred to are employed, the time taken for the evaporation of th solvent from the fabric located between the fastener members is very short, and consequently the material from which the members are made does not, to any appreciable extent, run into the interstices of this portion of the tape and the flexibility of the tape is not, therefore, destroyed.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. The process for the manufacture of sliding clasp fasteners of the kind described, consisting of casting the fastener members of suitable plastic material directly on the fabric mounting tape, and thereafter supplying a solvent by capillarity through the tape to the tape contacting portions of the fastener members for temporarily softening said tape contacting portions to enhance the firmness of adherence of said tape contacting portions to the tape.

2. The process as claimed in claim 1 in which the casting temperatures and pressures employed are sufficient to cause the material to assume the desired shape but insufiicient to cause the production of flash in substantial amount.

GEORGE HENRY CLIFFORD CORNER. 

